| 1. |
- Råberg, Tora, et al.
(author)
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Nitrogen balance in a stockless organic cropping system with different strategies for internal N cycling via residual biomass
- 2018
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In: Nutrient Cycling in Agroecosystems. - : Springer Netherlands. - 1385-1314 .- 1573-0867. ; 112:2, s. 165-178
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Journal article (peer-reviewed)abstract
- A major future challenge in agriculture is to reduce the use of new reactive nitrogen (N) while maintaining or increasing productivity without causing a negative N balance in cropping systems. We investigated if strategic management of internal biomass N resources (green manure ley, crop residues and cover crops) within an organic crop rotation of six main crops, could maintain the N balance. Two years of measurements in the field experiment in southern Sweden were used to compare three biomass management strategies: anaerobic digestion of ensiled biomass and application of the digestate to the non-legume crops (AD), biomass redistribution as silage to non-legume crops (BR), and leaving the biomass in situ (IS). Neither aboveground crop N content from soil, nor the proportion of N derived from N2 fixation in legumes were influenced by biomass management treatment. On the other hand, the allocation of N-rich silage and digestate to non-legume crops resulted in higher N2 fixation in AD and BR (57 and 58 kg ha−1 year−1), compared to IS (33 kg ha−1 year−1) in the second study year. The N balance ranged between − 9.9 and 24 kg N ha−1, with more positive budgets in AD and BR than in IS. The storage of biomass for reallocation in spring led to an increasing accumulation of N in the BR and AD systems from one year to another. These strategies also provide an opportunity to supply the crop with the N when most needed, thereby potentially decreasing the risk of N losses during winter. © 2018, The Author(s).
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| 2. |
- Råberg, Tora, et al.
(author)
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Productivity in an arable and stockless organic cropping system may be enhanced by strategic recycling of biomass
- 2019
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In: Renewable Agriculture and Food Systems. - : Cambridge University Press. - 1742-1705 .- 1742-1713. ; 34:1, s. 20-32
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Journal article (peer-reviewed)abstract
- Recirculation of nitrogen (N) from crop residue and green-manure biomass resources may reduce the need to add new reactive N to maintain crop yield and quality. The aim of this study was to determine how different strategies for recycling residual and green-manure biomass influence yield and N concentration of the edible parts of food crops in a stockless organic cropping system. For this purpose, three biomass distribution treatments were investigated in a field experiment, based on a cropping system designed to produce both high-quality food crops and biomass resources from crop residues, cover crops and a green-manure ley. The three treatments, applied at the cropping system level, were: (1) incorporating the aboveground biomass resources in situ (IS); (2) harvesting, ensiling and redistributing the same biomass resources to the non-legume crops (biomass redistribution, BR); and (3) harvesting, ensiling and using the biomass resources as substrate for production of bio-methane via anaerobic digestion (AD) followed by distribution of the digestate as bio-fertilizer to the non-legume crops. The redistribution of ensiled (BR) and digested (AD) biomass did not increase the yield of the edible parts in winter rye (Secale cereal L.), white cabbage (Brassica oleracea L.) or red beet (Beta vulgaris L.) compared with leaving the biomass on the ground at harvest (IS). The BR treatment increased the yield of lentil intercropped with oat, compared with IS treatment in one of the two studied years. The total biomass yield of the cover crop following winter rye was significantly higher in the BR treatment than in IS in both years. The legume proportion in the green-manure ley was significantly higher in the AD and BR treatments as compared with IS in one of the experimental years. This study showed that strategic biomass redistribution has the potential to enhance biomass productivity while maintaining food crop yields, thereby enhancing whole system productivity. Biomass redistribution systems both with and without biogas digestion offer a new strategy for the development of multifunctional arable cropping systems that rely on internal nutrient cycling.
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| 3. |
- Råberg, Tora
(author)
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Strategic nitrogen management in stockless organic cropping systems : redistribution of residual biomass for improved energy and nitrogen balance
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Agriculture faces the challenge of producing high yields to feed a growing world population, while simultaneously addressing environmental problems such as eutrophication, emissions of greenhouse gases, loss of biodiversity and soil degradation. Organic farming can be part of the solution, as it promotes biodiversity, uses less energy for fertiliser production and often has higher inputs of organic matter to soil than conventional farming. However, yields are often lower, partly due to asynchrony in mineralisation of organic nitrogen (N) and crop acquisition. Growing legumes for protein production and input of biological N2 fixation to supply the cropping system with N is a common practice on organic farms. The addition of reactive N to the agroecosystem via legumes may, just as with synthetic fertilisers, lead to N surpluses and environmentally harmful N losses. It is therefore important to improve N cycling within agricultural cropping systems. This thesis assessed the effects of strategic redistribution of residual biomass on productivity, crop quality, N balance, N and carbon (C) turnover, eutrophication potential and global warming potential in a stockless organic cropping system. A field experiment was established to test three strategies for recirculating N in residual biomass within a six-year crop rotation; 1) leaving crop residues in situ at harvest (IS), 2) biomass redistribution as silage to non-legume crops (BR) or 3) anaerobic digestion of the silage before redistribution (AD). A soil incubation experiment in a controlled environment was also performed, to measure mineralisation of N, soil respiration and greenhouse gas emissions from incorporation of fresh and anaerobically digested grass clover ley. Moreover, energy balance, greenhouse gas emissions and eutrophication potential in BR and AD were compared with those in IS in a life cycle assessment (LCA). Results from the field experiment showed that the BR and AD strategies maintained the same yields as IS, but resulted in higher N2 fixation in the legumes and consequently a more positive N balance. The soil incubation experiment showed that total C losses during 90 days after soil application of ley were higher than from digested ley. A major energy gain was achieved in AD, and a decrease in global warming potential compared to BR. There was a reduction in eutrophication potential with the strategic redistribution of silage and digestate (BR and AD), compared with IS. In conclusion these results show that strategic redistribution of biomass-based digestate can improve the N balance of crop rotations and produce a surplus of bioenergy, which are key elements for enhancing the sustainability of stockless organic cropping systems.
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| 4. |
- Råberg, Tora
(author)
-
Strategic nitrogen management in stockless organic cropping systems
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- A griculture faces the challenge of producing high yields to feed a growing world population, while simultaneously addressing environmental problems such as eutrophication, emissions of greenhouse gases, loss of biodiversity and soil degradation. Organic farming can be part of the solution, as it promotes biodiversity, uses less energy for fertiliser production and often has higher inputs of organic matter to soil than conventional farming. However, yields are often lower, partly due to asynchrony in mineralisation of organic nitrogen (N) and crop acquisition. Growing legumes for protein production and input of biological N2 fixation to supply the cropping system with N is a common practice on organic farms. The addition of reactive N to the agroecosystem via legumes may, just as with synthetic fertilisers, lead to N surpluses and environmentally harmful N losses. It is therefore important to improve N cycling within agricultural cropping systems. This thesis assessed the effects of strategic redistribution of residual biomass on productivity, crop quality, N balance, N and carbon (C) turnover, eutrophication potential and global warming potential in a stockless organic cropping system. A field experiment was established to test three strategies for recirculating N in residual biomass within a six-year crop rotation; 1) leaving crop residues in situ at harvest (IS), 2) biomass redistribution as silage to non-legume crops (BR) or 3) anaerobic digestion of the silage before redistribution (AD). A soil incubation experiment in a controlled environment was also performed, to measure mineralisation of N, soil respiration and greenhouse gas emissions from incorporation of fresh and anaerobically digested grass clover ley. Moreover, energy balance, greenhouse gas emissions and eutrophication potential in BR and AD were compared with those in IS in a life cycle assessment (LCA). Results from the field experiment showed that the BR and AD strategies maintained the same yields as IS, but resulted in higher N2 fixation in the legumes and consequently a more positive N balance. The soil incubation experiment showed that total C losses during 90 days after soil application of ley were higher than from digested ley. A major energy gain was achieved in AD, and a decrease in global warming potential compared to BR. There was a reduction in eutrophication potential with the strategic redistribution of silage and digestate (BR and AD), compared with IS. In conclusion these results show that strategic redistribution of biomass-based digestate can improve the N balance of crop rotations and produce a surplus of bioenergy, which are key elements for enhancing the sustainability of stockless organic cropping systems.
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